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Carbohydrates
Carbohydrates
glucose provides energy for the brain and ½ of energy for muscles and tissues
glycogen is stored glucose glucose is immediate energy glycogen is reserve energy
Carbohydrates
all plant food milk
carbohydrates are not equal–simple carbohydrates–complex carbohydrates
Simple Carbohydrates
sugars–monosaccharides – single sugars–disaccharides – 2 monosaccharides
Complex Carbohydrates
starches and fibers polysaccharides
–chains of monosaccharides
Simple Carbs monosaccharides
–all are 6 carbon hexes6 carbons12 hydrogens6 oxygensarrangement differs
–accounts for varying sweetness
–glucose, fructose, galactose
Glucose
mild sweet flavor known as blood sugar essential energy source found in every
disaccharide and polysaccharide
Fructose
sweetest sugar found in fruits and honey added to soft drinks,
cereals, deserts
Galactose
hardly tastes sweet rarely found
naturally as a single sugar
Disaccharides
pairs of the monosaccharides–glucose is always present–2nd of the pair could be fructose, galactose
or another glucose– taken apart by hydrolysis–put together by condensation–hydrolysis and condensation occur with all
energy nutrients–maltose, sucrose, lactose
Condensation
making a disaccharide– chemical reaction linking 2
monosaccharides
Hydrolysis
breaking a disaccharide–water molecule splits–occurs during digestion
Maltose
2 glucose units produced when starch breaks down not abundant
Sucrose fructose and
glucose tastes sweet
– fruit, vegetables, grains
table sugar is refined sugarcane and sugar beets
brown, white, powdered
Lactose
glucose and galactose main carbohydrate in
milk– known as milk sugar
Complex Carbohydrates
polysaccharides–glycogen and starch
built entirely of glucose– fiber
variety of monosaccharides and other carbohydrate derivatives
Glycogen limited in meat and not found in plants
–not an important dietary source of carbohydrate
BUT–all glucose is stored as glycogen– long chains allow for hydrolysis and release of energy
Starches
stored in plant cells body hydrolyzes plant starch to glucose
Fiber
structural parts of plants– found in all plant derived food
bonds of fibers cannot be broken down during the digestive process–minimal or no energy available
Fiber types
cellulose pectins lignins resistant starches
–classified as fibers–escape digestion and
absorption
Fiber Characteristics soluble fibers, viscous, fermentable
–easily digested by bacteria in colon–associated with protection against heart
disease and diabetes lower cholesterol and glucose levels
– found in legumes and fruits
Fiber
insoluble and not easily fermented–promote bowel movements–alleviate constipation– found in grains and vegetables
DRI and Fiber
distinguish fibers by source–dietary fibers: naturally in intact plants– functional fibers: extracted from plants or
manufactured– total fiber: sum of the 2
Carbohydrate Digestion
break down into glucose–body is able to absorb and use
large starch molecules– extensive breakdown
disaccharides–broken once
monosaccharides–don’t need to be broken down
Carbohydrate Digestion begins in mouth
–chewing releases saliva–enzyme amylase hydrolyzes starch to
polysaccharides and maltose stomach
–no enzymes available to break down starch
–acid does some breakdown– fibers in starch provide feeling of fullness
small intestine–majority of carbohydrate digestion
takes place here–pancreatic amylase reduces carbs to
glucose chains or disaccharides–specific enzymes finish the job
maltase–maltose into 2 glucose
sucrase–sucrose into glucose and fructose
lactase–lactose into glucose and
galactose
large intestine–1-4 hours for sugars and
starches to be digested–only fibers remain
attract water, which softens stool
–bacteria ferment some fiberswater, gas, short-chain
fatty acids (used for energy)
Carbohydrate Absorption
glucose can be absorbed in the mouth majority absorbed in small intestine
–active transportglucose and galactic
– facilitated diffusion fructosesmaller rise in blood glucose
Lactose Intolerance more lactose is consumed than can be
digested– lactose molecules attract water
cause floating, abdominal discomfort, diarrhea
– intestinal bacteria feed on undigested lactoseproduce acid and gas
Lactose Intolerance
age, damage, medication, diarrhea, malnutrition
management requires dietary change–6 grams (1/2 cup) usually tolerable– take in gradually–hard cheeses & cottage cheese–enzyme drops or tablets
lactose free diet is extremely difficult to accomplish
Carbohydrate Metabolism 1/3 of body’s glycogen is stored in liver
– released as glucose to bloodstream1. eat – intake glucose2. liver condenses extra glucose to glycogen3. blood glucose falls4. liver hydrolyzes glycogen to glucose
Glycogen is bulky, so we store only so much: short term energy supply
Fat is the long term energy supply.
Glucose for Energy
enzymes break apart glucose – yielding energy
inadequate supply of carbohydrates–ketone bodies (fat fragments) are an
alternate energy source during starvation–excess ketones can lead to ketosis:
imbalance of acids in body minimum of 50 – 100 grams of carbs/day
are needed to avoid ketosis
Glucose Homeostasis
maintaining an even balance of glucose is controlled by insulin and glucagon– insulin
moves glucose into the blood–glucagon
brings glucose out of storage
maintaining balance–balanced meals at regular intervals
fiber and some fat slow the digestive process down
glucose gets into the blood slow and steady
Maintaining Blood
Glucose Homeostasis
IntestineWhen a person eats,blood glucose rises.
1
2
Insulin stimulates the uptake of glucose into cells and storageas glycogen in the liver andmuscles. Insulin also stimulatesthe conversion of excessglucose into fat for storage.
3
4
5
6
7 Blood glucose begins torise.
a The stress hormoneepinephrine and other hormonesalso bring glucose out of storage.
GlucoseInsulinGlucagonGlycogen
Glucagon stimulates livercells to break down glycogenand release glucose into theblood.a
Liver
Low blood glucose stimulatesthe pancreas to releaseglucagon into the bloodstream.
As the body's cells useglucose, blood levels decline.
Glucagon
Pancreas
Fat cell
Liver
Muscle
High blood glucose stimulatesthe pancreas to release insulin.
Pancreas
Insulin
Imbalance
diabetes–after food intake, blood glucose rises and
is not regulated because insulin is inadequate
hypoglycemia–blood glucose drops dramatically
too much insulin, activity, inadequate food intake, illness
diet adjustment includes fiber-rich carbs and protein
Glycemic Index
way of classifying food according to their ability to raise blood glucose
much controversy
Sugar
½ comes from natural sources, ½ from refined and added–sucrose, corn syrup, honey
excess can lead to nutrient deficiencies and tooth decay–empty calories–sugar and starch break down in the
mouth
Sugar
recommended intake–added sugar = no more than 10% of energy
intake
Starch and Fiber
diet that includes starch, fiber and natural sugars–whole grains, vegetables, legumes, fruits
may protect against heart disease and stroke
reduces the risk of type 2 diabetesenhances the health of the large
intestinecan promote weight loss
Starch and Fiber starch intake
–45-65%–225 – 325 grams (DV is 300
grams)–900-1300 kcal/2000 kcal–RDA is 130 grams
fiber intake–Daily Value is 25 grams/2000
kcal
Groceries
grains: 1 serving = 15 grams vegetables
–½ cup starchy = 15 grams–½ cup nonstarchy = 5 grams
fruit: 1 serving = 15 grams milk: 1 cup = 12 grams meat: none or little legumes: ½ cup = 15 grams
Artificial Sweeteners
help keep sugar and energy intake down anything we eat has FDA approval
–saccharin–aspartame–acesulfame potassium–sucralose–neotame
Sugar Replacers
sugar alcohols–provide bulk and sweetness
cookies, gum, candy, jelly–do contain minimal kcal– low glycemic response
absorbed slowly–do not cause dental caries